Reactivation of latent CMV is frequently observed in recipients of solid organ and bone marrow transplants and is a significant cause of morbidity and mortality in immunocompromised hosts. Due to the species specificity of HCMV, investigation of the factors that induce reactivation in transplant recipients has been hampered by the lack of appropriate models that recapitulate the complexity of the in vivo environment. Therefore, we have used MCMV as a model to study latency and reactivation. Whereas we have previously focused on immunocompetent mouse models, we have more recently developed a new transplant model for reactivation of infectious virus, in which kidneys from latently infected mice are transplanted into immunocompromised NOD.Cg-PrkdcscidIL2rgtm1Wjl/Szj (NSG) recipients, which lack functional B, T, and NK cells. Reactivation in this model occurs slowly and sporadically over a period of 2-6 weeks, and results in a disseminated infection that spreads from the transplanted kidney to other recipient organs. The kinetics of reactivation in this model is similar to that observed in transplant recipients treated with standard immunosuppression protocols. Thus, our new model is highly relevant to the clinical setting of CMV disease and allows us to explore novel mechanisms responsible for primary CMV infection in transplant recipients. We hypothesize that reactivation in this model is due to activation of viral gene expression initiated by ischemia/reperfusion (I/R) injury, which leads to a sterile inflammatory response mediated by innate immune cells. I/R injury causes formation of damage associated molecular patterns (DAMPs), which are recognized by pattern recognition receptors on innate immune cells, up-regulation of chemokines that recruit inflammatory cells, which cause further damage through release of reactive oxygen and nitrogen species and proteolytic enzymes, and cytokines that activate signaling pathways leading to activation of transcription factors that control MCMV immediate early gene expression. In the absence of an adaptive immune response, we hypothesize that this leads to reactivation of infectious virus. In this application we propose to characterize markers of injury in this model and to investigate the requirement for neutrophils and macrophages in reactivation. In addition, we will investigate the therapeutic efficacy of activated protein C in blocking reactivation. This protein is currently in use clinically for prevention of kidney injury. These translational studies could provide the basis for clinical trials to investigate novel therapies to prevent reactivation of CMV from latency in immunocompromised patients. PUBLIC HEALTH RELEVANCE: Cytomegalovirus (CMV) is a ubiquitous herpesvirus which establishes a lifelong latent infection, and reactivation of latent virus can cause significant morbidity or mortality in immunocompromised patients. The goal of this application is to understand cellular mechanisms leading to reactivation of murine cytomegalovirus in immunocompromised transplant recipients. These studies may lead to development of new therapies to prevent reactivation of latent CMV and its sequelae.